a) Field of the Invention
This invention relates to finely divided pigments, and has an object thereof the provision of finely divided pigments useful for various applications, for example, as pigments for printing inks (gravure inks, offset inks, flexographic inks, etc.), plastic colorants, pigment-type textile printing agents, pigments for paints, image recording agents, and pigments for image displaying. The term xe2x80x9cpigmentxe2x80x9d as used herein means an aggregate of fine coloring particles, whereas the term xe2x80x9cpigment particlesxe2x80x9d as used herein means xe2x80x9cfine coloring articles making up a pigmentxe2x80x9d. Further, the term xe2x80x9csecondary particlesxe2x80x9d as used herein means particles formed by agglomeration of finely divided pigment particles (primary particles) and having greater particle sizes.
b) Description of the Related Art
Pigments have conventionally been used as coloring agents for paints, printing inks, plastics and the like. In each of these pigments, fine particles (primary particles) which make up the pigment have already undergone agglomeration, and the agglomerated particles (secondary particle) have particles sizes around 10 to 20 xcexcm. A pigment formed of particles of such large particle sizes cannot be used as a coloring agent for paints or printing inks. Therefore, the pigment is used after mechanically milling or grinding it together with a paint vehicle or a printing ink varnish in a pigment dispersing machine, for example, a ball mill, sand mill, attritor, horizontal continuous disperser with tumbling medium contained therein, vertical continuous disperser with tumbling medium contained therein, kneader or three-roll mill such that particles making up the pigment are dispersed with particle sizes of from about 0.5 to 0.2 xcexcm in the vehicle or varnish.
In applications where dyes have been employed as coloring agents to date, pigments have been finding increasing utility in recent years for their excellent lightfastness and waterproofness. These applications include, for example, inks for writing instruments, in which aqueous dyes or oil-soluble dyes have been used as coloring agents, and colorants for plastics, in which oil-soluble dyes have been used as coloring agents as transparency is required. Further, there are also increasing demands for pigments as coloring agents for LCD color filters, coloring agents for ink-jet recording inks and coloring agents for color toners.
For these applications, it is necessary to divide pigment-forming particles (pigment particles) as finely as possible (0.1 xcexcm or smaller). As a method for finely dividing pigment particles, it is known to use a high-speed sand mill or the like. Further, to provide a colored article with transparency and vividness or sharpness, it is necessary to finely divide pigment particles and at the same time, to sift pigment particles to control their sizes (to make their particle size distribution narrower). Moreover, it is also important to evenly disperse the finely divided pigment particles in a vehicle and during storage of the dispersion, to provide the dispersion with stability such that the pigment particles remain in their finely divided form without undergoing agglomeration.
An object of the present invention is, therefore, to provide a finely divided pigment, which is usable not only as a coloring agent for paints, printing inks, plastics and the like but also as a coloring agent for LCD color filters, ink-jet recording inks, color toners and the like to obtain colored products having a transparent, vivid and sharp color hue and also properties such as excellent lightfastness, outstanding weatherability and superb heat resistance. Another object of the present invention is to provide a coloring composition comprising the finely divided pigment as a colorant.
To achieve the above-described objects, the present inventors have proceed with an extensive investigation. As a result, it has been found that irrespective of the kind of a pigment, the above-described objects can be achieved by finely dividing the pigment particles to obtain a particular particle size distribution, leading to the completion of the present invention
In one aspect of the present invention, there is thus provided a finely divided pigment formed of an aggregate of primary particles, wherein a number of primary particles of not greater than 0.1 xcexcm in particle size is at least 95% of an entire number of the primary particles, and a number of primary particles of greater than 0.1 xcexcm in particle size is at most 5% of the entire number of the primary particles.
In another aspect of the present invention, there is also provided a process for producing the finely divided pigment, which comprises grinding a parent pigment together with a water-soluble inorganic salt and a water-soluble organic solvent in a grinding machine at a temperature of from 30 to 90xc2x0 C. for 2 to 6 hours under a load, and then removing the water-soluble inorganic salt and the water-soluble organic solvent.
In a further aspect of the present invention, there is also provided a coloring composition comprising a dispersing medium and the finely divided pigment dispersed in the dispersing medium. The coloring composition may be an image recording agent for the ink-jet recording system, an image recording agent for the electronic printing or electrostatic recording system, or a coloring agent for forming color filter pixels.
In a further aspect of the present invention, there is also provided a process for coloring an article, which comprises using the coloring composition.
In a still further aspect of the present invention, there is also provided an image recording apparatus of the ink-jet recording system or the electronic printing or electrostatic recording system, comprising the image recording agent for the ink-jet recording system or the image recording agent according for the electronic printing or electrostatic recording system mounted as an image recording agent.
In a still further aspect of the present invention, there is also provided a process for manufacturing a color filter, which comprises forming a color pattern on a color filter substrate by using the coloring agent for forming color filter pixels.
In a yet further aspect of the present invention, there is also provided a color filter manufactured by the manufacturing process.
When the finely divided pigment according to the present invention is used as a coloring agent in plastics, pigment-type textile printing agents, printing inks, paints, especially metallic paints, or the like, the finely divided pigment exhibits, on colored products or articles, excellent dispersion and superb properties such as weatherability, lightfastness and heat resistance while retaining transparency, vividness and sharpness comparable with dyes. In addition, the finely divided pigment according to the present invention is also useful as a pigment in image recording agents for the ink-jet recording system, image recording agents for the electronic printing or electrostatic recording system and coloring agents for forming pixels on color filters.
The present invention will hereinafter be described in further detail based on certain preferred embodiments.
The finely divided pigment according to the present invention is characterized in that the number of primary particles of not greater than 0.1 xcexcm in particle size is at least 95% of the entire number of the primary particles, and the number of primary particles of greater than 0.1 xcexcm in particle size is at most 5% of the entire number of the primary particles. When fastness, such as heat resistance and weatherability, of the pigment is taken into consideration, the number of primary particles of not greater than 0.02 xcexcm in particle size may preferably be at most 10% of the entire number of the primary particles. By finely dividing the pigment particles into such a particle size range, it is possible to provide a colored product with both a color hue having transparency, vividness and sharpness and excellent fastness such as heat resistance and weatherability. The term xe2x80x9cnumberxe2x80x9d as used herein means the number of all particles or the number of particles in a specific particle size range as counted under a transmission electron microscope as will be mentioned below.
Pigments to which the present invention is applicable include all pigments known to date. Preferred examples can include organic pigments such as soluble or insoluble azo pigments, high molecular azo pigments, quinacridone pigments, anthraquinone pigments, diketopyrrolopyrrole pigments, quinophthalone pigments, methine/azomethine pigments, phthalocyanine pigments, perylene pigments, perinone pigments, isoindolinone pigments and metal complex pigments.
Among the above-described pigments, those capable of exhibiting particularly excellent advantageous effects by finely dividing their particles can include: as yellow pigments, C.I. Pigment Yellow (hereinafter abbreviated as xe2x80x9cPYxe2x80x9d)-74, PY-83, PY-93, PY-94, PY-95, PY-97, PY-109, PY-110, PY-120, PY-128, PY-138, PY-139, PY-147, PY-150, PY-151, PY-154, PY-155, PY-166, PY-175, PY-180, PY-181, PY-185, PY-191, etc.; as orange pigments, C.I. Pigment Orange (hereinafter abbreviated as xe2x80x9cPOxe2x80x9d)-61, PO-64, PO-71, PO-73, etc.; as red pigments, C.I. Pigment Red (hereinafter abbreviated as xe2x80x9cPRxe2x80x9d)-4, PR-5, PR-23, PR-48:2, PR-48:4, PR-57:1, PR-112, PR-122, PR-144, PR-146, PR-147, PR-150, PR-166, PR-170, PR-177, PR-184, PR-185, PR-202, PR-207, PR-214, PR-220, PR-221, PR-242, PR-254, PR-255, PR-264, PR-272, etc; as blue pigments, C.I. Pigment Blue (hereinafter abbreviated as xe2x80x9cPBxe2x80x9d)-15:1, PB-15:2, PB-15:3, PB-15:4, PB-15:5, PB-15:6, PB-16, PB-17:1, PB-60, aluminum phthalocyanine blue, etc.; as green pigments, C.I. Pigment Green (hereinafter abbreviated as xe2x80x9cPGxe2x80x9d)-7, PG-36, etc.; and as violet pigments, C.I. Pigment Violet (hereinafter abbreviated as xe2x80x9cPVxe2x80x9d)-19, PV-23, PV-37, etc.
The particle sizes and number fractions of the particles making up the finely divided pigment, said particle sizes and number fractions characterizing the present invention, can be determined by observing the pigment particles at xc3x9730,000 to xc3x97100,000 magnification under a transmission electron microscope and counting the number of particles of not greater than 0.1 xcexcm in particle size, the number of particles of greater than 0.1 xcexcm in particle size and the number of particles of smaller than 0.02 xcexcm in particle size among the whole particles in a field of view. This procedure is performed three times on samples of the same pigment. With respect to each of the samples, the numbers of particles in the above-described specific ranges are counted. The particle sizes and number fractions of the pigment particle are then calculated by averaging the results of the counting.
The finely divided pigment according to the present invention, which has the above-described number distribution of the fractions of primary particles, can be obtained by finely dividing a parent pigment (pre-division pigment) by a method specifically suited for the pigment. Some methods will hereinafter be described as examples. It should however be borne in mind that the present invention is not limited to these methods.
(1) A description will first be made of so-called solvent salt milling. According to this method, a parent pigment is charged together with a water-soluble inorganic salt, such as sodium chloride or sodium sulfate, and a water-soluble organic solvent, such as ethylene glycol, diethylene glycol or polyethylene glycol, in appropriate mixing proportions in a kneader. After the contents are kneaded for a predetermined time at a controlled temperature while applying a load to the contents to compress the same, the kneaded mixture is added to a heated aqueous solution of dilute sulfuric acid and is stirred. The kneaded mixture is collected by filtration, and is then washed with water to remove the water-soluble inorganic salt and the water-soluble organic solvent. The filtration residue is then dried by hot air or the like. Instead of this method, dry milling making use of a ball mill or an oscillating mill can also be used in a similar manner as described above. In this case, a grinding medium such as steel balls or steel rods is used, and if necessary, an inorganic salt can be used as a grinding aid. As the grinding aid, aluminum nitrate or the like can be mentioned in addition to the above-described sodium chloride and sodium sulfate.
Grinding conditions for obtaining the finely divided pigment according to the present invention, which has the above-described number distribution of the fractions of primary particles, differ depending on the kind of the pigment. Concerning the proportions of the water-soluble inorganic salt, parent pigment and water-soluble organic solvent, the kneading time and the processing temperatures, it is, therefore, important to determine optimal conditions and optimal proportions depending upon the kind of the pigment and to conduct the finely dividing processing under the conditions so determined.
When the contents of the grinding apparatus are pressed during the grinding of the pigment, substantial frictional heat is generated under strong shear force so that particles which make up the pigment may undergo crystal growth into greater particles. When pressing as described above, it is thus necessary to adequately cool the grinding machine to avoid heating of its contents or to add a crystal growth inhibitor for the pigment particles such as a solid resin which dissolves at least partially in the water-soluble organic solvent. This makes it possible to obtain the finely divided pigment according to the present invention.
Described in more detail, when a parent pigment formed of particles having primary particle sizes of from 0.1 to 0.8 xcexcm or so is used as a raw material for the finely divided pigment according to the present invention, it is desired to use the water-soluble inorganic salt in a proportion 2 to 10 times by weight, preferably 3 to 6 times by weight as much as the parent pigment and the water-soluble organic solvent in a proportion 0.5 to 2.0 times by weight, preferably 1.0 to 1.5 times by weight as much as the parent pigment and to control the temperature of the contents of the grinding machine or kneader at 30 to 90xc2x0 C. The required grinding or kneading time may range generally from 2 to 6 hours, although it differs depending upon the combination of the proportions of the inorganic salt and water-soluble organic solvent and the temperature of the contents. Further, the finely divided pigment according to the present invention, which has a desired particle size distribution, can be obtained in a shorter time as the proportion of the inorganic salt to be used becomes greater and as the processing temperature becomes lower.
(2) There is also a method called xe2x80x9cacid pastingxe2x80x9d. According to this method, a parent pigment is dissolved in a good solvent for the pigment, such as sulfuric acid or polyphosphoric acid, and the resulting solution is poured into a poor solvent such as water to make pigment particles deposit or precipitate. The finely divided pigment according to the present invention can be obtained only by thoroughly washing the thus-obtained pigment with water. However, the objects of the present invention can be more surely achieved by conducting treatment of the pigment particles with an adequate organic solvent or the like and if necessary, making combined use of solvent salt milling, which has been described above under (1), such that the particle sizes of the pigment particles are controlled into a narrower range.
(3) Especially for azo pigments, a method is also known as disclosed in JP 60-36224 B or JP 3055673 B. Described specifically, upon subjecting the diazonium salt of a specific diazotizable aromatic amine and a coupling component to a coupling reaction, at least two kinds of coupling components are used to produce a finely divided pigment. This is a method called xe2x80x9cco-couplingxe2x80x9d, which is specific to azo pigments. In some instances, the finely divided pigment according to the present invention can be obtained as desired only by this method. Preferably, however, combined use of the solvent salt milling method described above under (1) is a surer method for obtaining the finely divided pigment according to the present invention.
The finely divided pigment according to the present invention obtained as described above has a color hue excellent in vividness, sharpness and transparency on or in a colored product and further, exhibits excellent fastness properties such as outstanding weatherability, superb heat resistance and excellent solvent resistance on or in the colored product.
The finely divided pigment according to the present invention can be used inter alia as a coloring agent for inks containing vehicles such as resins, paints, pigment-type textile printing agents, fibers, and molded or otherwise formed plastic products, a coloring agent for image recording, and a coloring agent for image displaying. Upon employment for an application, the finely divided pigment according to the present invention is used as a coloring composition with the pigment dispersed in a dispersing medium which is commonly used in the application. In the composition, the primary particles which make up the finely divided pigment exist as independent particles (primary particles) or slightly agglomerated particles (secondary particles). It is desired to prepare the coloring composition such that the average particle size of the pigment particles dispersed in the coloring composition is reduced generally to 0.2 xcexcm or smaller, preferably to 0.15 xcexcm or smaller.
It is well known that finely divided pigment particles generally become susceptible to agglomeration in a dispersing medium when their surface energy increases extremely. By subjecting the finely divided pigment particles to surface treatment with a surfactant or a pigment derivative (a compound obtained by introducing desired substituent group(s) into a compound which has the same chemical structure as the pigment but has not been formed into a pigment) or by adding one or more of various dispersants to the dispersing medium such as a vehicle with the pigment dispersed therein, the pigment particles can be prevented from agglomeration to avoid an increase in the viscosity of a pigment dispersion (a liquid mixture with the pigment dispersed in the dispersing medium) and also to assure the stability of dispersion of the pigment particles.
Upon preparing the coloring composition by using the finely divided pigment according to the present invention, one or more of various pigment derivatives can be used in combination to improve the dispersibility of the pigment particles and the flowability of the pigment dispersion although the finely divided pigment according to the present invention can be used singly. Illustrative of pigment derivatives usable in the present invention are anthraquinone compound derivatives with aliphatic N-substituted alkylamine residual groups introduced into anthraquinone compounds as disclosed in JP 11-189732 A and JP 2000-193817 A; and phthalocyanine compound derivatives with aliphatic N-substituted alkylamine residual groups introduced into phthalocyanine compounds as disclosed in JP 2000-136333 A. No particular limitation is imposed on the proportion of such a pigment derivative to be used. In general, however, the pigment derivative may be used in a proportion of from 0.5 to 50 wt. %, with a proportion of from 1 to 30 wt. % being preferred, both based on the finely divided pigment according to the present invention.
In the present invention, a dispersant can be used in place of the above-described pigment derivative or together with the pigment derivative as needed to improve the dispersibility of the pigment particles in the dispersing medium. As the dispersant, any one or more of conventionally known dispersants can be used. Illustrative are polyester oligomers having aliphatic hydroxycarboxylic acid residual groups as disclosed in JP 7-96654 B and JP 7-207178 A; organosiloxane polymers (e.g., xe2x80x9cKP341xe2x80x9d, trade name, product of Shin-Etsu Chemical Co., Ltd.); (meth) acrylic acid (co)polymers (e.g., xe2x80x9cPolyflow No. 75xe2x80x9d, xe2x80x9cPolyflow No. 90xe2x80x9d and xe2x80x9cPolyflow No. 95xe2x80x9d, trade names, products of Kyoei Yushi Kagaku Kogyo K.K.); cationic surfactants (e.g., xe2x80x9cW001xe2x80x9d, trade name, product of Yusho K.K.); nonionic surfactants, for example, polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether, polyethylene glycol dilaurate, polyethylene glycol distearate, and sorbitan fatty acid esters; anionic surfactants (e.g., xe2x80x9cW004xe2x80x9d, xe2x80x9cW005xe2x80x9d and xe2x80x9cW017xe2x80x9d, trade names, product of Yusho K.K.); various SOLSPERSE dispersants such as xe2x80x9cSOLSPERSE 3000xe2x80x9d, xe2x80x9cSOLSPERSE 5000xe2x80x9d, xe2x80x9cSOLSPERSE 9000xe2x80x9d, xe2x80x9cSOLSPERSE 12000xe2x80x9d, xe2x80x9cSOLSPERSE 13240xe2x80x9d, xe2x80x9cSOLSPERSE 13940xe2x80x9d, xe2x80x9cSOLSPERSE 17000xe2x80x9d, xe2x80x9cSOLSPERSE 20000xe2x80x9d, xe2x80x9cSOLSPERSE 24000xe2x80x9d, xe2x80x9cSOLSPERSE 26000xe2x80x9d and xe2x80x9cSOLSPERSE 28000xe2x80x9d, trade names, products of Zeneca Inc.; and xe2x80x9cISONET S-20xe2x80x9d, trade name, product of Sanyo Chemical Industries, Ltd. No particular limitation is imposed on the proportion of the dispersant to be used. In general, however, the dispersant may be used in a proportion of from 0.1 to 50 wt. %, with a proportion of from 0.1 to 20 wt. % being preferred, both based on the finely divided pigment according to the present invention.
When using the finely divided pigment according to the present invention as a coloring composition with the pigment dispersed in a dispersing medium for a particular application, any one of dispersing media commonly employed in the particular application can be used as the dispersing medium, and no particular limitation is imposed on the dispersing medium. Further, no particular limitation is imposed on the proportion of the finely divided pigment in the coloring composition, and the finely divided pigment can be used in similar proportions as conventionally known proportions in respective applications. In general, however, the content of the finely divided pigment in the coloring composition may range from 1 to 60 wt. % or so although it varies depending on the application.
The dispersing medium will now be exemplified. For example, a dispersing medium for paints can be either solid or liquid. As a liquid dispersing medium, water, a water-hydrophilic organic solvent mixture, or an organic solvent can be used. As the organic solvent, aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, esters, ketones, glycol ethers, alcohols and the like are used, for example, and no particular limitation is imposed thereon.
When a vehicle for paints, a varnish for printing inks or a vehicle for coating formulations is used as a dispersing medium, a conventionally known, oily or aqueous dispersing medium is used depending on each application. Examples of the dispersing medium can include alkyd resins of long oil length, medium oil length or short oil length, modified alkyd resins such as phenol-modified alkyd resins and styrenated alkyd resins, aminoalkyd resins, oil-free alkyd resins, baking acrylic resins, acrylic lacquer resins, acrylic polyol resins, polyester resins, epoxy resins, butylated melamine resin, methylated melamine resin, urea-melamine resin, phenol resin, rosin-modified phenol resin, rosin-modified maleic acid resin, polyurethane resins, styrene resin, styrene-acrylic acid or acrylic acid ester copolymer resins, styrene-diene copolymer resins, vinyl chloride copolymer resins, polyvinyl acetate resin, vinyl acetate copolymer resins, ethylene-vinyl acetate copolymer resin, ethylene-vinyl acetate copolymer resin, butyral resin, petroleum resins, rosin esters, modified resins such as maleic rosin esters, drying oils, and boiled oils.
Examples of solid dispersing media (for example, molded or otherwise formed products) can include various plastics such as polyethylene resin, polypropylene resin, polyvinyl chloride resin, styrene resin, acrylonitrile-styrene copolymer resin, polyester resins, acrylic resins, methacrylic acid or methacrylic acid ester-styrene copolymer resins, and ABS resin. When fibers are a dispersing medium, illustrative are pre-spinning fiber materials such as nylon, polyethylene terephthalate, polybutylene terephthalate, polypropylene and polyimides.
As dispersing media in ink-jet recording inks for image recording, there are water and mixtures of water and water-soluble organic solvents. Usable examples of such water-soluble organic solvents can include alcohols (e.g., methanol, ethanol, and isopropyl alcohol); polyhydric alcohols (e.g., ethylene glycol, diethylene glycol, polyethylene glycol, and glycerin); alkyl ethers of polyhydric alcohols (e.g., ethyleneglycol monomethylether, and ethyleneglycol monobutylether); amines (e.g., diethanolamine, and ethanolamine); and heterocyclic compounds (e.g., N-methyl-2-pyrrolidone, and sulfolane). In addition, the above dispersing media ink-jet recording inks can include water-soluble resins (e.g., acrylic resins, methacrylic acid-styrene copolymer resins, polyester resins, polyamide resins, and polyurethane resins, or mixtures of thereof).
Further, as examples of dispersing media in (image recording) developers or toners for electrophotographic copying machines, polystyrene resin, styrene-(meth)acrylic acid ester copolymer resins, styrene-butadiene copolymer resin, polyester resins and epoxy resins are used together with various additives. In general, dispersing media for use in (image displaying) coloring agents for LCD color filters are each composed of an organic solvent, which contains a film-forming resin, and a pigment dispersant. Examples of resins usable in these dispersing media can include photosensitive cyclized rubber resins, photosensitive phenol resins, photosensitive polyacrylate resins, photosensitive polyamide resins, photosensitive polyimide resins, unsaturated polyester resins, polyester-acrylate resins, polyepoxy-acrylate resins, polyurethane-acrylate resins, polyether-acrylate resins, and polyol-acrylate resins. As reactive diluents, various monomers can be added.
The present invention will next be described more specifically based on Examples and Comparative Examples, in which the designations xe2x80x9cpartxe2x80x9d or xe2x80x9cpartsxe2x80x9d and xe2x80x9c%xe2x80x9d are each on a weight basis unless otherwise specifically indicated. Further, each xe2x80x9c%xe2x80x9d in each particle size distribution of pigment particles means xe2x80x9cpercentage in terms of the number of particlesxe2x80x9d. The fractions (percentages in terms of the number of particles) of pigment particles in each particle size distribution are based on the numbers of the pigment particles in the fractions observed under a transmission electron microscope.